An endoscopic procedure is a minimally invasive surgical technique where an endoscope is inserted into the body through a small incision or body opening. In general, endoscopic procedures tend to produce shorter recovery times, a reduced risk of infection, and reduced scarring as compared with conventional surgical techniques. However, endoscopic procedures also often require greater precision and skill of the personnel who actually perform the procedure.
A typical endoscope includes an optical system capable of imaging the surgical field. Some endoscopes include a utility lumen (a tube-like channel) through which a wide range of diagnostic and/or treatment devices can be passed, including optical laser fibers. Some endoscopes, such as cystoscopes, provide little in the way of stability features through which the fiber is disposed and supported, and thus require an additional stability element to be supplied with the fiber.
Many currently employed endoscopic surgical procedures involve delivering laser energy to a surgical field through an endoscope for the purpose of, for example, making an incision, fragmenting kidney stones or removing tissue. Holmium laser enucleation of the prostate (HoLEP) is one such procedure, which is used to treat benign prostatic hyperplasia (BPH) by removing tissue from the prostate. Laser lithotripsy, used to fragment kidney stones, is another. In both of these examples, an optical fiber, which is disposed through the endoscope, is used to deliver energy generated by an externally-positioned laser to the treatment site within the patient's body.
The optical fiber commonly used to deliver the laser energy in procedures such as lithotripsy and HoLEP is known in the art as a “straight fire” laser fiber. The laser fiber is typically comprised of a series of layers, including: a) an optical “core” most commonly made of silica; b) a “clad” (sometimes referred to as the primary clad) that covers the core and is typically made up of a fluorinated silica; c) a clear “coating” (sometimes referred to as the secondary clad) that covers the primary clad and is typically made of a low index acrylate; and d) a jacket that covers and protects the coating or secondary clad, typically comprised of ethylene tetrafluoroethylene (ETFE). The diameter of the core for these fibers can typically range from 150 to 1,000 microns.
During an ureteroscopy procedure (e.g. lithotripsy), a medical practitioner can insert an ureteroscope into a patient's urinary tract, for example, over a guide wire to locate an undesirable object such as a kidney stone or a bladder stone. Once the stone is located, an optical fiber can be introduced into the utility lumen (i.e. working channel) of the ureteroscope and advanced until a portion of the distal end of the optical fiber, called a tip, comes into contact with or in close proximity to the stone. A red or green aiming beam is emitted from the tip of the optical fiber to target the object. Electromagnetic radiation from, for example, a holmium (Ho) laser can also be directed through the optical fiber towards the stone to break the stone into fragments. The fragments can then be removed with a retrieval device via the working channel or flushed through normal urinary activity.
Ureteroscopes generally have an outside diameter of approximately 9 French and have a very small working channel, which requires a small optical fiber (typically having a core diameter in the range of 150 to 365 microns). The smaller the fiber diameter, the more fragile is the fiber. Many known optical fibers that are used in ureteroscopy procedures are supplied by manufacturers with approximately 4 mm of the jacket and coating stripped off of the distal end, thereby exposing the silica core and clad (this area forms the tip). The coating layer, which is necessary to protect the core and clad, is partially or completely removed when the Jacket is stripped off. Therefore, the tip is susceptible to damage and moisture degradation, which is the reason manufacturers tend to limit the stripped length to approximately 4 mm.
During use, the hard silica core and fluorinated silica clad forming the tip slowly chips away until the 4 mm tip is completely gone (this process is known as burn-back). The core, clad and coating are translucent, which can be difficult for the operator to see when firing the laser. However, the jacket is opaque, making it easy to view during use. This is another reason why manufacturers limit the length of their tips to 4 mm. This length ensures that the proximate end of the tip, which ends where the jacket has not been removed, provides the operator a reference regarding the remaining length of the tip. Once the tip is consumed, continued use eventually causes the jacket to fray, thus impeding the ability to aim the laser. Therefore, if the fiber burns back to the jacket during, and prior to completion of, a procedure, the procedure must be delayed while the fiber is removed from the ureteroscope, an additional 4 mm of jacket is stripped off and the fiber is reinserted through the working channel of the ureteroscope to continue the procedure.
Thus, medical personnel must not only be skilled in the use of the endoscope and the laser fiber in performing the surgical procedure, but they must also be able handle removal of the fiber from the endoscope, stripping of the jacket layer to create a new tip, and then the re-installation of the fiber into the endoscope, all without damaging or compromising the efficacy of the fiber so that the procedure may be ultimately completed successfully. This is not a simple task, as the OD (outside diameter) of the fibers is very small, so the glass fibers are delicate and the jacket layer is thin.
HoLEP procedures typically require a core optical fiber having a diameter of 550 microns. In this procedure, the fiber is passed through a stability sheath that is secured inside a cystoscope with a 24 or 26 French outside diameter. Burn-back of the fiber's tip occurs at an even faster rate during HoLEP procedures. To remove prostate tissue, the laser is operated at much higher energy (about 100 watts) and for a longer duration relative to other procedures. Thus, to accommodate the increased burn-back during the procedure, this procedure requires a substantially longer (i.e. up to 10 cm) tip than the 4 mm tip typically provided by the manufacturer. As a result, medical personnel must first strip off approximately 10 cm of the jacket just prior to initiating the procedure. This is sometimes difficult to do in an OR setting and often results in broken tips and delays. Stripping an optical fiber just prior to use also requires the use of a sterile fiber optic stripper, which a hospital may not have.
After removing the Jacket, the fiber is inserted into a stability sheath which is used to guide the laser fiber through the scope and to the target. This because the cystoscope does not include a utility lumen through to pass the fiber. Typical stability sheaths are over 30 cm in length, having an outside diameter of approximately 7.5 French with a blunt tip. Prior to inserting the cystoscope into the patient, the stability sheath is inserted through an elastomeric seal at the proximal end of the cystoscope and is pushed through a positioning ring located inside the distal end of the cystoscope. The inside diameter of the locating or positioning ring is approximately 8 French.
The medical practitioner guides the stability sheath through the positioning ring until the distal end of the stability sheath is flush with the distal end of the scope. Maintaining this flush position can be difficult while advancing the fiber to the target. Often, misalignment of the stability sheath with the ring during insertion occurs, because there is no line of sight during the insertion. This misalignment leads to the stability sheath butting up against the proximal end of the positioning ring making it difficult to feed through the ring. The cystoscope is comprised of 2 main parts, the camera and the optical system that is inserted into an outer tube (or cannula) and locked into place. It is common for medical personnel to briefly separate the optical portion of the scope from the scope cannula to visualize the distal end of the stability sheath, to aid in aligning the sheath as it is pushed through the scope cannula and into the positioning ring.
In summary, there are a number of reasons that manufacturers of laser fibers limit the length of the tips provided therewith to about 4 mm. First, the tips are vulnerable to damage and moisture compromise prior to use. The longer the tips, the greater is that vulnerability. In addition, tips that extend longer than about 4 mm will force the line where the jacket begins (at the distal end of the tip) to be outside of the surgical view, making it harder to gauge how far the tip extends from the end of the scope as its length is consumed by burn-back. Yet, certain procedures require tips significantly longer than 4 mm standard size to be completed without interruption. Moreover, it requires medical personnel to be skilled enough to strip the jacket layer to establish a new tip, either during a procedure where the tip has been completely consumed back to the jacket, or prior to commencing the procedure because it is known that a much longer tip length will be required before the procedure is even initiated.
Laser Fibers that require a stability sheath for support within certain endoscopes are often difficult to insert into a guide feature or ring, and further require that alignment with the end of the scope be performed manually by the operator performing the procedure.